1. Field of the Invention
This invention generally relates to strainers for initially removing most of the liquid and solid particles from a contaminated gas stream, and is particularly useful when combined with fiberglass filters which filter out the remaining very fine liquid mist and solid particles that remain in the gas stream after it passes through the strainer.
2. Prior Art
The separation of suspended liquid particles from a gas stream can be accomplished using various separators or desiccant beds. From conventional type scrubbers, separators, or mist extractors, the gas stream may carry over finely divided solid particles and aerosol-sized fogs or mists of free water, hydrocarbons, and other chemicals. The solid particles may consist of iron and silica compounds. The liquid may consist of water, hydrocarbon mist such as compressor lube oil, gasoline plant absorption oil, and field distillate depending on the type of upstream equipment. Amine based chemical inhibitors may be also present due to corrosion preventive treatment of upstream producing wells.
When using desiccant beds, molecular weight hydrocarbons will plug the micro pores of the desiccant particles thereby reducing their ability to absorb water. Repeated regeneration of a bed will cause the formation of coke which fouls the bed by sealing the surface of the desiccant particles. Some of the light crudes tend to polymerize due to a catalytic reaction with impure desiccants which can also cause bed fouling. Free water slugs will severely shatter the desiccant particles causing excessive pressure drop across the bed. The shattered particles may also be carried over into the gas stream in the form of desiccant dust which may damage downstream equipment. Aerosol salt water mists will evaporate during bed regeneration, leaving salts that plug up the micro pores of the desiccant. Absorbed amine from corrosion inhibitors will decompose and form ammonia compounds during the bed regeneration cycle. The ammonia chemically reacts with the desiccant causing loss in its activity.
The above mentioned problems are especially acute since gas wells are now being produced at or close to their maximum production rates. This tends to increase the amount of water, crude oil, and liquid hydrocarbons produced with the gas. Also, there is often an increased amount of sand, iron sulfides, and other solid contaminants entrained in the produced gas. Thus, as a result of the increased production from gas wells, the gas produced therefrom is often wetter and dirtier than would be the case if the well was produced at a reduced rate. Due to the increasing need for gas, however, it is nevertheless highly desirable to produce the wells at or close to their maximum possible production rates, and therefore it is necessary to provide improved means for removing the contaminants entrained in the gas so that only clean and very dry gas will be delivered to the pipeline.
Relatively recently liquid separators have been adapted using upstream a coalescer-filter section followed downstream by a very fine liquid separator section. The coalescer filters are supposed to remove most of the solid particles and liquid droplets from the gas before the gas is delivered to the separator section. The filters comprise perforated tubular casings covered with sleeves formed of a graded-density fiberglass material through which the gas is passed. The gas flows from the outside to the inside casing of each filter element. The very small porosity of the fiberglass material can cause any liquid mist entrained in the gas to coalesce into larger drops and fall out of the gas stream. The fiberglass also removes solid particles down to a size of under one micron.
Coalescer elements can be very efficient in removing liquid in the form of mist and the very small solid particles carried by a gas stream, but, when used as above described, the outer surfaces of the filters become contaminated prematurely by the foreign matter, thereby sealing the outer layers of the fiberglass. The fiberglass material can also become overloaded by an arriving slug of water. When the solid foreign matter in the outside layers of the fiberglass plugs up its pores, the coalesced liquid drops also tend to saturate the fiberglass. A saturated fiberglass filter must be replaced, and such replacement is relatively expensive. For example, one filter element may cost $50 or more, not counting the downtime cost for the equipment.
It is also known to use a centrifugal separator followed by a coalescer filter. But in such a unit the filter would also overload on account of the relative inefficiency of the separator. Thus, the coalescer filter can only be used in conjunction with a very efficient liquid remover or separator, and such separator was not available prior to this invention.
It is very important, therefore, that as much of the liquid and solid particles as possible be removed from the gas upstream of the coalescer stage, using means not subject to overloading, to thereby extend the useful life of the coalescer fiberglass elements, say having to replace them once a year instead of once a month, which constitutes a considerable financial saving.
It is a more specific object of this invention to provide a conically-shaped punched metallic strainer having a plurality of holes whose inner edges have perforation teeth resulting from the punching operation. The angle of the conic wall and the solidity portion of the strainer are selected to build up a desired pressure drop thereacross. The liquid drops flowing over the inner surface of the strainer and the liquid particles precipitated from the gas as a result of the pressure drop across the wall of the strainer collect around the perforation teeth which serve as barriers or "dams" for the liquid pools collected thereabout. When the volume of a particular pool becomes large enough, it will overflow causing large liquid drops to be jetted out through its adjacent hole to the outside of the strainer. Such motion is caused both by gravity and by the pressure drop across the punched wall of the strainer.